Add initial implementation for namespace packages

Also needs more tests and docs

src/_pytest/pathlib.py

@@ -761,12 +761,13 @@ def resolve_pkg_root_and_module_name(
     """
     pkg_path = resolve_package_path(path)
     if pkg_path is not None:
-        pkg_root = pkg_path.parent
-        # pkg_root.parent does not contain a __init__.py file, as per resolve_package_path,
-        # but if it is reachable from sys.argv, it should be considered a namespace package.
         # https://packaging.python.org/en/latest/guides/packaging-namespace-packages/
-        if consider_ns_packages and str(pkg_root.parent) in sys.path:
-            pkg_root = pkg_root.parent
+        pkg_root = pkg_path.parent
+        if consider_ns_packages:
+            for parent in pkg_path.parents:
+                if str(parent) in sys.path:
+                    pkg_root = parent
+                    break
         names = list(path.with_suffix("").relative_to(pkg_root).parts)
         if names[-1] == "__init__":
             names.pop()

testing/test_pathlib.py

@@ -647,6 +647,29 @@ def test_resolve_pkg_root_and_module_name(
             "src.app.core.models",
         )
 
+    def test_resolve_pkg_root_and_module_name_ns_multiple_levels(
+        self, tmp_path: Path, monkeypatch: MonkeyPatch
+    ) -> None:
+        (tmp_path / "src/com/company/app/core").mkdir(parents=True)
+        (tmp_path / "src/com/company/app/__init__.py").touch()
+        (tmp_path / "src/com/company/app/core/__init__.py").touch()
+        models_py = tmp_path / "src/com/company/app/core/models.py"
+        models_py.touch()
+
+        monkeypatch.syspath_prepend(tmp_path / "src")
+
+        pkg_root, module_name = resolve_pkg_root_and_module_name(
+            models_py, consider_ns_packages=True
+        )
+        assert (pkg_root, module_name) == (
+            tmp_path / "src",
+            "com.company.app.core.models",
+        )
+
+        mod = import_path(models_py, mode="importlib", root=tmp_path)
+        assert mod.__name__ == "com.company.app.core.models"
+        assert mod.__file__ == str(models_py)
+
     def test_insert_missing_modules(
         self, monkeypatch: MonkeyPatch, tmp_path: Path
     ) -> None: